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bioplasticsMAGAZINE_1101

From Science & Research

From Science & Research Biomaterials Based on Article contributed by Marguerite Rinaudo Centre de recherches sur les Macromolécules Végétales (CNRS) affiliated with Joseph Fourier University Grenoble, France Chitin (poly-β -(14)-N-acetyl-D-glucosamine) is a natural renewable polysaccharide of major importance first identified in 1884 (Fig. 1). This biopolymer is widely synthesized in a number of living organisms and, considering the amount of chitin produced annually on a world scale, it is the second most abundant polymer after cellulose [1,2]. Despite the widespread occurrence of chitin, it seems that up until now the main commercial source of chitin comes from crab and shrimp shells. In industrial processes chitin is extracted from crustaceans by acid treatment to dissolve calcium carbonate followed by alkaline extraction for the solubilisation of proteins. In addition a decolourisation step is often applied to remove the residual pigments and obtain a colourless product. These treatments need to be adapted to each chitin source due to differences in the ultrastructure of the initial sources. The resulting chitin needs to be graded in terms of purity and colour since residual proteins and pigments can cause problems for further utilization (thermal treatment, allergic reactions….). After partial deacetylation under strong alkaline conditions chitosan is obtained, which is the most important chitin derivative in terms of applications and availability. Chitosan is a random copolymer of β-(14)-N-acetyl-D-glucosamine and β-(14)-D-glucosamine (Fig. 1). Depending on the utilization, these polymers may be processed in different forms such as sponge, bead, film, fibre, solution, aerosol, or gel, as soon as soluble systems can be obtained; they may also be mixed with other natural or synthetic polymers to obtain blends or composites with original properties. Chitin characterization and main properties. Chitin is a semi-crystalline polysaccharide in which the chitin chains are tightly held by a number of inter-chain and intra-chain hydrogen bonds; this is the reason for good physical performances but also for difficulties in processing (just as cellulose, chitin is infusible and difficult to solubilise) [1]. The question of their solubility is a major problem in view of the development of processing and uses of chitin. The mostly used solvent for a long time was DMAc/LiCl; this solvent is also used to determine the molecular weight of chitin [1]. CaCl 2 .2H 2 O-saturated MeOH as well concentrated phosphoric acid, lithium thiocyanate or NaOH at low temperature were also proposed. From solution, chitin is able to be regenerated (in water or other non-solvents) under the different forms (casting of films and extrusion of fibres) or mixed with cellulose or other polymers to obtain blends (interesting blends may be developed after solubilisation of cellulose and chitin in common solvents) [3,4]. The main difficulties with chitin are the quality and reproducibility of the samples supplied, but also the difficulty to solubilize. 48 bioplastics MAGAZINE [01/11] Vol. 6

From Science & Research Chitin and Chitosan Chitin, as other polysaccharides including cellulose, have good film and fibre forming properties; in addition, the good stability of chitin-based materials is promoted by the establishment of an H-bond network between extended chains. Chitin adds original properties to the new materials as being biocompatible, non-allergic, biodegradable, nontoxic, with antimicrobial activity and low immunogenicity, deodorizing, moisture controlling; it is also insoluble in water whatever the pH, with some hydrophilic character. Recently, a short review presented the applications of chitin and chitosan-based nano-materials [5]. Chemical modifications are performed using the same methods as for cellulose or other polysaccharides (reaction on the –OH positions). Chitosan characterization and main properties. Chitosan results from the deacetylation of chitin under alkaline conditions or by enzymatic hydrolysis in the presence of a chitin deacetylase. It becomes soluble in aqueous acidic media (pH

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